Multiple QD-LED sub-pixels for high on-axis brightness and low colour shift

ABSTRACT

A light emitting structure comprises a bank surrounding a sub-pixel stack on a substrate, a first filler material in an interior space above the sub-pixel stack, and a second filler material over the first filler material. The sub-pixel stack emits a first emission peak along an on-axis direction substantially normal to a top surface of the sub-pixel stack and through an interface between the first and second filler materials. The sub-pixel stack emits a second emission peak along an off-axis direction that is totally internally reflected by the interface before reaching a sloped sidewall of the bank and is then emitted along the on-axis direction. An emissive area of the sub-pixel stack is configured such that the second emission peak is reflected by the interface not more than once before reaching the sloped sidewall.

FIELD

The present disclosure generally relates to layers and bank structuresused for emissive devices, in particular for Quantum Dot (QD) LightEmitting Diode (LED) displays. In particular, the present disclosureseeks to improve efficiency, reduce colour shift, and improve on-axisbrightness for top emitting structures embedded in a high refractiveindex encapsulate material surrounded by a bank.

BACKGROUND

An Organic Light Emitting Diode (OLED) is among the most prevalent LEDsused in a display device while quantum dots are proposed as animprovement to OLEDs as they have better spectral emission and arechemically more stable. Quantum dots are often used as phosphors forblue LEDs and exist as backlight for Liquid Crystal Displays (LCDs).Conventional LED displays take a refining approach with cavities in theLED structure and their effect on light. For example, Kodak(US20060158098) describes a top emitting structure and Samsung (U.S.Pat. No. 9,583,727) describes an OLED and QLED structure with lightemitting regions between reflective areas, one of which is partiallytransmitting.

Other displays involve methods to improve luminance of cavities in LEDs.For example, Samsung (US2015/0084012) describes the use of dispersivelayers in an OLED structure, Samsung (U.S. Pat. No. 8,894,243) describesthe use of microstructure scattering to improve efficiency, and 3M(WO2017/205174) describes enhancement of light emission by use ofsurface plasmon nanoparticles or nanostructures in transport layers.

Methods that involve modifications to a cavity (or cavities) are oftendifficult to implement as they require very small size features orcontrol of layers. One alternative to modifying the cavity is to use athick top “filler” layer with a high refractive index, which enablesreduction in Fresnel reflections and increases in transmissivity througha top electrode. However, the light in a high index layer may be mostlytrapped by total internal reflection (TIR). To extract the trappedlight, reflective and/or scattering banks surrounding the filler layerare used to out-couple light that is trapped by TIR.

TCL (CN106876566) and JOLED (U.S. Pat. No. 9,029,843) describe such apixel arrangement with banks and a filler material above the organiclayers of the cavity and between the banks. Hitachi (U.S. Pat. No.7,091,658) describes banks that can be reflective using electrodemetallic material, Cambridge Display Tech (KR1020150020140) describesbanks that can be shaped in different structures using differentassembly steps, and Sharp (U.S. Pat. No. 10,090,489) describes a shapedreflector underneath the organic layers.

Another approach is to control filler materials. For example, GlobalOLED (U.S. Pat. No. 8,207,668) describes filler layers that can becontrolled, where the fillers and organic layers have differentthicknesses for different sub pixels, in order to maximize the lightoutput as a function of wavelength.

In yet another approach, Lee et al. (“Three Dimensional PixelConfigurations for Optical Outcoupling of OLED Displays—OpticalSimulation”, Proceedings SID Display Week 2019) describes simulations ofpixel banks structures with the design of an OLED emission layer. Suchapproach simulates optimum extraction efficiencies with bank structuresthat maximize efficiency for real bank structures. The optimum solutioninvolves only green light and an ITO electrode, which would not bepractical in such a device as the emission spectrum would be too broad,and thus have an inferior colour gamut while On-axis brightness(apparent brightness to the user) is not considered.

In yet another approach, red, green, or blue pixels are split intomultiple sub-pixels. Each sub-pixel is not independently controlled, andthe sub-pixels emit equally according to the required emission at aspecific pixel. For example, Japan Display (JP6274771) describes adisplay where the sub-pixels are split equally for both colours.Semiconductor Energy Laboratories (U.S. Pat. No. 8,587,742) describessuch split arrangement offset by colours. Shenzhen Yunyinggu TechnologyCo., Ltd. (U.S. Pat. No. 10,103,205) describes an OLED display with twored and green sub-pixels and only one blue pixel.

In yet another approach, arrangements of sub-pixels can also beasymmetric between colours as described in Japan Display Inc. (U.S. Pat.No. 9,680,133). In another approach, the shapes of each pixels can alsobe irregular, for example, Japan Display Inc. (U.S. Pat. No. 9,337,242)describes red, green, blue and white pixels that are arranged in“stripes” across a rectangular pixel or BOE (U.S. Pat. No. 10,401,691)describes the pixels that are alternate parallelograms.

In yet another approach, sub-pixel structuring is more unusual, forexample, BOE (US2017/0110519) describes different sub pixels havingdifferent cavity designs to reduce colour shift effects. In anotherapproach, Lockheed Martin Corp. (US 2019/0103518) describes stackedemitting areas in a hexagonal shape to produce white light.

CITATION LIST

-   U.S. Pub. No. US 2006/0158098 A1 (Eastman Kodak Company, published    Jul. 20, 2006).-   U.S. Pat. No. 9,583,727 B2 (Samsung Display Co. Ltd., patented Feb.    28, 2017).-   U.S. Pub. No. US 2015/0084012 A1 (Samsung Display Co. Ltd, published    Mar. 26, 2015).-   U.S. Pat. No. 8,894,243 B2 (Samsung Corning Precision Materials Co.    Ltd., patented Nov. 25, 2014).-   International Pub. No. WO2017/205174 A1 (3M Innovative Properties    Company, published Nov. 30, 2017).-   Chinese Pub. No. CN106876566 A (TCL, published Jun. 20, 2017).-   U.S. Pat. No. 9,029,843 B2 (JOLED Inc., patented May 12, 2015).-   U.S. Pat. No. 7,091,658 B2 (Hitachi, patented Aug. 15, 2006).-   Korean No. KR1020150020140 (Cambridge Display Tech, published Feb.    25, 2015).-   U.S. Pat. No. 10,090,489 B2 (Sharp Kabushiki Kaisha, patented Oct.    2, 2018).-   U.S. Pat. No. 8,207,668 B2 (Global OLED Technology LLC, patented    Jun. 26, 2012).-   Lee et al. (“Three Dimensional Pixel Configurations for Optical    Outcoupling of OLED Displays—Optical Simulation”, Proceedings SID    Display Week 2019, published 2019).-   Japan Pat. No. JP 6274771 (Japan Display Inc., patented Feb. 7,    2018).-   U.S. Pat. No. 8,587,742 B2 (Semiconductor Energy Laboratory Co.,    Ltd., patented Nov. 19, 2013).-   U.S. Pat. No. 10,103,205 B2 (Shenzhen Yunyinggu Technology Co.,    Ltd., patented Oct. 16, 2018).-   U.S. Pat. No. 9,680,133 B2 (Japan Display Inc., patented Jun. 13,    2017).-   U.S. Pat. No. 9,337,242 B2 (Japan Display Inc., patented May 10,    2016).-   U.S. Pat. No. 10,401,691 B2 (BOE Technology Group Co., Ltd.,    patented Sep. 3, 2019).-   U.S. Pub. No. US 2017/0110519 A1 (BOE Technology Group Co., Ltd.,    published Apr. 20, 2017).-   U.S. Pub. No. US 2019/0103518 A1 (Lockheed Martin Corp., published    Apr. 4, 2019).

SUMMARY

The present disclosure relates to multiple QD-LED sub-pixels for highon-axis brightness and low colour shift.

In accordance with one aspect of the present disclosure, a lightemitting structure comprises a substrate, a sub-pixel stack over asurface of the substrate, a bank surrounding the sub-pixel stack andforming an interior space above the sub-pixel stack, a first fillermaterial in the interior space and having a first refraction index, anda second filler material over the first filler material and having asecond refractive index lower than the first refractive index, and aninterface between the first filler material and the second fillermaterial. The sub-pixel stack emits a first emission peak into the firstfiller material along an on-axis direction substantially normal to a topsurface of the sub-pixel stack and emits a second emission peak into thefirst filler material along an off-axis direction at an angle to theon-axis direction, the first emission peak is emitted through theinterface substantially without total internal reflection, the secondemission peak is totally internally reflected by the interface beforereaching a sloped sidewall of the bank, and the second emission peak isreflected by the sloped sidewall and emitted through the interface alongthe on-axis direction without substantial total internal reflection. Anemissive area of the sub-pixel stack is configured such that the secondemission peak is reflected by the interface not more than once beforereaching the sloped sidewall of the bank.

In some implementations, a minimum width of the emissive area of thesub-pixel stack is configured based on a thickness of the first fillermaterial, and the angle between the on-axis direction of the firstemission peak and the off-axis direction of the second emission peak.

In some implementations, the first emission peak is emitted through theinterface along the on-axis direction in a central region of the lightemitting structure, the second emission peak reflected by the slopedsidewall of the bank is emitted through the interface along the on-axisdirection in a peripheral region of the light emitting structure, andon-axis brightness is increased and off-axis colour shift having anangle is reduced.

In some implementations, the first emission peak is emitted through theinterface along the on-axis direction in a peripheral region of thelight emitting structure adjacent to a bottom edge of the bank, thesecond emission peak reflected by the sloped sidewall of the bank isemitted through the interface along the on-axis direction in anotherperipheral region of the light emitting structure opposite of theperipheral region, and on-axis brightness is increased and off-axiscolour shift having an angle is reduced.

In some implementations, the light emitting structure further comprisesanother sub-pixel stack arranged immediately adjacent to the sub-pixelstack, and the another sub-pixel stack emits the first emission peak andthe second emission peak and has an emissive area substantially equal tothe emission area of the sub-pixel stack.

In some implementations, the sub-pixel stack and the another sub-pixelstack are controlled to a same control signal.

In some implementations, the second filler material has a secondrefractive index substantially equal to or lower than a first refractiveindex of the first filler material.

In some implementations, the emissive area has one of the followingshapes, a rectangular shape, a square shape, an elliptical shape, acircular shape, and a triangular shape.

In some implementations, an angle between the sloped sidewall of thebank and the top surface of the sub-pixel stack is one-half the anglebetween the on-axis direction of the first emission peak and theoff-axis direction of the second emission peak.

In some implementations, the sub-pixel stack comprises an emissive layerbetween a first transport layer and a second transport layer, a firstelectrode layer coupled to the first transport layer; and a secondelectrode layer coupled to the second transport layer.

In some implementations, the emissive layer includes quantum dotemission material, the first transport layer includes a hole transportlayer, the second transport layer includes an electron transport layer,the first electrode layer is an anode layer including a metallicreflector for reflecting the light emitted from the emissive layer, andthe second electrode layer is a cathode layer including a non-metallicand substantially transparent material.

In some implementations, the emissive layer includes quantum dotemission material, the first transport layer includes an electrontransport layer, the second transport layer includes a hole transportlayer, the first electrode layer is a cathode layer having a metallicreflector for reflecting the light emitted from the emissive layer, andthe second electrode layer is an anode layer having a non-metallic andsubstantially transparent material.

In accordance with another aspect of the present disclosure, a displaydevice comprises a light emitting structure. The light emittingstructure comprises a substrate, a sub-pixel stack over a surface of thesubstrate, a bank surrounding the sub-pixel stack and forming aninterior space above the sub-pixel stack, a first filler material in theinterior space and having a first refraction index, and a second fillermaterial over the first filler material and having a second refractiveindex lower than the first refractive index, and an interface betweenthe first filler material and the second filler material. The sub-pixelstack emits a first emission peak into the first filler material alongan on-axis direction substantially normal to a top surface of thesub-pixel stack and emits a second emission peak into the first fillermaterial along an off-axis direction at an angle to the on-axisdirection, the first emission peak is emitted through the interfacesubstantially without total internal reflection, the second emissionpeak is totally internally reflected by the interface before reaching asloped sidewall of the bank, and the second emission peak is reflectedby the sloped sidewall and emitted through the interface along theon-axis direction without substantial total internal reflection. Anemissive area of the sub-pixel stack is configured such that the secondemission peak is reflected by the interface not more than once beforereaching the sloped sidewall of the bank.

In accordance with another aspect of the present disclosure, a lightemitting structure comprises a substrate, a plurality of sub-pixelstructures over the substrate, each of the plurality of sub-pixelstructures having a same emissive area. At least one of the plurality ofsub-pixel structures includes a sub-pixel stack over the substrate, abank surrounding the sub-pixel stack on the substrate and forming acavity above the sub-pixel stack, a first filler material in the cavity,and a second filler material over the first filler material, the secondfiller material having a second refractive index substantially equal toor lower than a first refractive index of the first filler material. Thesub-pixel stack emits a first emission peak along an on-axis directionsubstantially normal to a top surface of the sub-pixel stack, and asecond emission peak along an off-axis direction at an angle to theon-axis direction, the first emission peak emits through an interfacebetween the first filler material and the second filler materialsubstantially without reflection, the second emission peak from thesub-pixel stack is totally reflected by the interface onto a slopedsidewall of the bank, and the second emission peak reflected from thesloped sidewall of the bank emits along the on-axis direction throughthe interface substantially without reflection, and the second emissionpeak is reflected by the interface not more than once before reachingthe sloped sidewall of the bank.

In some implementations, a minimum width of the emissive area isconfigured based on a thickness of the first filler material, and theangle between the on-axis direction of the first emission peak and theoff-axis direction of the second emission peak.

In some implementations, an angle between the sloped sidewall of thebank and the top surface of the sub-pixel stack is one-half the anglebetween the on-axis direction of the first emission peak and theoff-axis direction of the second emission peak.

In some implementations, the emissive areas of the plurality ofsub-pixel structures are substantially the same, and have one of thefollowing shapes, a rectangular shape, a square shape, an ellipticalshape, a circular shape, and a triangular shape.

In some implementations, the sub-pixel stack comprises an emissive layerbetween a first transport layer and a second transport layer, a firstelectrode layer coupled to the first transport layer; and a secondelectrode layer coupled to the second transport layer.

In some implementations, the emissive layer includes quantum dotemission material, the first transport layer includes a hole transportlayer, the second transport layer includes an electron transport layer,the first electrode layer is an anode layer including a metallicreflector for reflecting the light emitted from the emissive layer, andthe second electrode layer is a cathode layer including a non-metallicand substantially transparent material.

In some implementations, the emissive layer includes quantum dotemission material, the first transport layer includes an electrontransport layer, the second transport layer includes a hole transportlayer, the first electrode layer is a cathode layer having a metallicreflector for reflecting the light emitted from the emissive layer, andthe second electrode layer is an anode layer having a non-metallic andsubstantially transparent material.

BRIEF DESCRIPTION OF DRAWINGS

Aspects of the example disclosure are best understood from the followingdetailed description when read with the accompanying figures. Variousfeatures are not drawn to scale. Dimensions of various features may bearbitrarily increased or reduced for clarity of discussion.

FIG. 1A is a schematic cross-sectional view of a portion of an examplelight emitting structure in accordance with an example implementation ofthe present disclosure.

FIG. 1B is a schematic cross-sectional view of a portion of thesub-pixel stack in the light emitting structure of FIG. 1A in accordancewith an example implementation of the present disclosure.

FIG. 2A illustrates a portion of an example light emitting structure inaccordance with an example implementation of the present disclosure.

FIG. 2B illustrates an example angular distribution diagram of a singleemission peak at one wavelength as measured in the example lightemitting structure of FIG. 2A in accordance with an exampleimplementation of the present disclosure.

FIG. 2C illustrates a portion of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 2D illustrates example angular distributions of three emissionpeaks measured in the example light emitting structure of FIG. 2C inaccordance with an example implementation of the present disclosure.

FIG. 3 illustrates example angular distribution diagrams from a lightemitting structure in accordance with an example implementation of thepresent disclosure.

FIG. 4A is a schematic cross-sectional view of an example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 4B, FIG. 4C, and FIG. 4D are detailed schematic cross-sectionalviews of three example structures of three sub-pixel stacks in the lightemitting structure of FIG. 4A in accordance with example implementationsof the present disclosure.

FIG. 5 is a schematic cross-sectional view of an example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 6 is a schematic cross-sectional view of another example lightemitting structure in accordance with an example implementation of thepresent disclosure.

FIG. 7A is a schematic cross-sectional view of another example lightemitting structure in accordance with an example implementation of thepresent disclosure.

FIG. 7B is a schematic cross-sectional view of another example lightemitting structure in accordance with an example implementation of thepresent disclosure.

FIG. 8A is a schematic perspective view of another example lightemitting structure in accordance with an example implementation of thepresent disclosure.

FIG. 8B is a schematic top view of the example light emitting structureof FIG. 8A in accordance with an example implementation of the presentdisclosure.

FIG. 9A is a schematic top view of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 9B is a schematic cross-sectional view of the example lightemitting structure of FIG. 9A along the line A-A′ in accordance with anexample implementation of the present disclosure.

FIG. 10 is a schematic top plan view of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 11 is a schematic top view of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 12 is a schematic top plan view of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

FIG. 13 is a schematic top plan view of another example light emittingstructure in accordance with an example implementation of the presentdisclosure.

DESCRIPTION

The following disclosure contains specific information pertaining toexample implementations in the present disclosure. The drawings in thepresent disclosure and their accompanying detailed description aredirected to merely example implementations. However, the presentdisclosure is not limited to merely these example implementations. Othervariations and implementations of the present disclosure will occur tothose skilled in the art.

Unless noted otherwise, like or corresponding elements among the figuresmay be indicated by like or corresponding reference numerals. Moreover,the drawings and illustrations in the present disclosure are generallynot to scale, and are not intended to correspond to actual relativedimensions.

For the purposes of consistency and ease of understanding, like featuresmay be identified (although, in some examples, not shown) by the samenumerals in the example figures. However, the features in differentimplementations may be differed in other respects, and thus shall not benarrowly confined to what is shown in the figures.

The description uses the phrases “in one implementation,” or “in someimplementations,” which may each refer to one or more of the same ordifferent implementations. The term “comprising” means “including, butnot necessarily limited to” and specifically indicates open-endedinclusion or membership in the so-described combination, group, seriesand the equivalent. The expression “at least one of A, B and C” or “atleast one of the following: A, B and C” means “only A, or only B, oronly C, or any combination of A, B and C.”

Additionally, for the purposes of explanation and non-limitation,specific details, such as functional entities, techniques, protocols,standard, and the like are set forth for providing an understanding ofthe described technology. In other examples, detailed description ofwell-known methods, technologies, systems, architectures, and the likeare omitted so as not to obscure the description with unnecessarydetails.

The present disclosure relates to an emissive display involving aquantum dot electro-emissive material in a light emitting diode (LED)arrangement. The LED arrangement typically includes a layer of quantumdot (QD) emission material (e.g., emissive layer) sandwiched between anelectron transport layer (ETL) and a hole transport layer (HTL). Thethree layers are sandwiched between two conductive layers to form asub-pixel stack. In one or more implementations of the presentdisclosure, a “top” emitting (TE) structure is used. The TE structureinvolves light emission from a side of the TE structure opposite a glasssubstrate on which the TE structure is disposed.

In one or more implementations of the present disclosure, fabrication ofa TE device involves one thick layer of conductive reflective material,typically, made of a metal (e.g., silver or aluminium) deposited on theglass substrate with the HTL layer on the conductive reflective layer(e.g., a reflective conductor or reflective electrode), the emissivelayer on the HTL layer, the ETL layer on the emissive layer, and atransparent electrode layer on the ETL layer. In one preferredimplementation, the reflective electrode has a thickness greater than 80nm (i.e., 10{circumflex over ( )}-9 meters). In another preferredimplementation, the reflective electrode includes a layer of silverhaving a thickness of approximately 100 nm and a layer of Indium TinOxide (ITO) having a thickness of approximately 10 nm. In one preferredimplementation, the HTL layer is made of a layer of PEDOT:PSS(poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) approximately40 nm thick and a layer of TFB(poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine))having a thickness of approximately 35-45 nm on the PEDOT:PSS layer. Inanother preferred implementation, an approximately 20 nm thick emissivelayer is disposed on the HTL layer and the ETL layer is disposed on theemissive layer. In another preferred implementation, the ETL layer ismade of Zinc Oxide (ZnO) nanoparticles and has a thickness ofapproximately 30-80 nm. In one preferred implementation, the transparentelectrode layer is a thin metal layer thick enough to carry sufficientcurrent yet thin enough to be transparent to light and disposed on theETL layer. In one preferred implementation, the transparent electrodelayer is an ITO layer having a thickness of approximately 80 nm.

In one or more implementations of the present disclosure, angularemission distributions from the emissive layer can be determined by adistance between the emissive layer and the reflective electrode layer(e.g., at the bottom of the sub-pixel stack) and the distance isdirectly dependent on a total thickness of the HTL layer. The distancebetween the emissive layer and the reflective electrode layer may betuned such that there are two directions of light emissions from thelight source where constructive interference occurs. One direction is anon-axis emission (e.g., emission normal to a plane, or a top surface, ofthe sub-pixel stack) and the other direction is an off-axis emission(e.g., emission is at an angle with respect to the on-axis direction).

In an example implementation where the reflective electrode is a perfectmirror, the reflective electrode layer is at a distance of a wavelength(e.g., λ) apart from the emissive layer. The distance may be 0.5, 1, orany integer with a multiple of 0.5 wavelength apart from the emissivelayer. In an example implementation where the reflective electrode isnot a perfect mirror (e.g., in other words a phase shift exists), apoint of reflection will not be located exactly at the surface of thereflective electrode. In one or more implementations of the presentdisclosure, the reflective electrode is, for example, at a distance ofabout 1 wavelength apart from the emissive layer in order generate twoemissions (e.g., on-axis and off-axis emissions). However, in order tooffset the effects of the phase shift in the reflective electrode, thedistance is adjusted to 0.87 wavelength. The emissive layer may generatea constructive on-axis emission normal to the reflective electrode andan off-axis emission at approximately 50° off-axis with respect to theon-axis emission such that a thickness of the HTL layer may be obtained.

The correlation described previously between the distance, thickness,angular emissions, and wavelength may be represented by the followingequations:2(d−d′)cos(θ_(P))=N*λ  Equation (1)d=T  Equation (2)where d is a sum of all optical thicknesses of all layers (e.g., 104 d 1and 104 d 2 in FIG. 1B) in the HTL layer, d′ is an optical distance froma top surface of the reflective electrode to an interior portion of thereflective electrode where effective reflection takes place (e.g., d′ inFIG. 1B), θ_(P) is an angle between the on-axis emission and theoff-axis emission (e.g., FIG. 1A), N is an integer greater than zero, λis wavelength in free space, and T is a total thickness of the HTL layerwhich may include one or more layers (e.g., TFB layer and PEDOT:PSSlayer) with each layer having a different refractive index. WithEquations (1) and (2), the thickness T can be tuned accordingly. In anexample implementation, N may equal to 1 to give a broad forwardemission direction. In a preferred example implementation, N may equalto 2 if d is predetermined and θ_(P) equals to 0 (e.g., d−d′=λ). Assuch, if cos(θ_(P)) equals to ½ (e.g., θ_(P) is 60°), a second peak maybe generated. Due to the difference in refractive indices betweenvarious elements (e.g., HTL layer, filler layer, etc.) of the presentdisclosure, θ_(P) is less than 60° in one preferred implementation, andθ_(P) is about 50°-55° in yet another preferred implementation). Theterm “emission” described in the present disclosure may refer to adistribution of wavelengths emitted, but is not limited to a singlewavelength. The term “wavelength” in the present disclosure may be usedto describe a peak or central wavelength amongst the plurality ofwavelengths in the context of equations above, but is not limited to thedescription provided herein.

The present disclosure is not limited to the provided examples as theessential principle of the disclosed structure still applies if thearrangement of the ETL and HTL layers are reversed. In a preferredimplementation of the present disclosure, the thickness of whichevertransport layer is between the emitting layer and the base (opaque)reflector on the substrate.

The example implementations of the present disclosure may be related toQLED structures. However, the present disclosure is not limited only toQLED structures and may be applicable to various implementations relatedto OLED structures.

In QLED sub-pixels, an interior space structure (e.g., a cavitystructure) may be outlined by a sub-pixel stack and a bank structuresurrounding the sub-pixel stack. A filler material with higherrefractive index may be disposed in the interior space structure abovethe sub-pixel stack. The bank structure may have a height that is, atleast, the same as or higher than the filler material with highrefractive index. The bank structure may also be lower in height withrespect to the filler material in some implementations. The fillermaterial with higher refractive index may extract more light from theinterior space than a layer directly above the filler material with lowrefractive index. The low refractive index layer is disposed over thefiller material to prevent optical crosstalk by preventing light frombeing coupled to the neighbouring pixels by an upper glass layerdisposed above the low refractive index layer. The low refractive indexlayer traps light in the filler material that is more readily absorbed.Therefore, light can be extracted more effectively from the fillermaterial without coupling light into the upper glass layer. In one ormore implementations, the low refractive index layer may be at least oneof an air gap, siloxane based nano-composite polymers from Inkron withrefractive index as low as 1.15, Poly(1,1,1,3,3,3-hexafluoroisopropylacrylate) with a refractive index of 1.375, andPoly(2,2,3,3,4,4,4-heptafluorobutyl acrylate) with a refractive index of1.377.

In the present disclosure, with the interior space structure and the toptransparent electrode, a distance between the emissive layer and thereflective electrode is tuned as described previously such that thereare on-axis emissions and off-axis emissions. The off-axis emissionswill be reflected onto the top surface (e.g., an interface) of thefiller material via total internal reflection (TIR) at least once beforebeing reflected off a sloped-surface of the bank and emitted through thefiller material along the on-axis direction. The bank structure at endsof each pixel is designed such that a sloped angle of the bank structure(e.g., bank angle) is one-half an angle of an off-axis emission into thefiller material relative to the on-axis emission.

In the present disclosure, light emitted from the cavity structure inthe direction to be reflected will then propagate to the bank byreflection from the filler surface and the original cavity. In general,as the incident direction of light from the filler top surface is thesame as the emission, the absorption in the cavity will be higher thanat other angles. Thus, absorption and weakening of the propagated lighthas consequences, such as a reduced efficiency and collimation, areduced mixing of on-axis and off-axis light emission and thus poorercolour shift off-axis, and a weak tolerance to the size of the sub-pixeland colour matching.

In the present disclosure, the efficiency, peak brightness, and colourshift of an emissive display may be affected by the number of times anoff-axis emission emitted from the an emissive area (e.g., a top surfacearea) of sub-pixel stack are reflected within the cavity (e.g., incidentupon the filler material immediately above the sub-pixel stack) beforereaching the bank since the propagated light is absorbed duringpropagation through the filler material.

In various implementations of the present disclosure, the size of theemissive area of a sub-pixel is configured such that light emission fromthe centre of the sub-pixel in at least one direction from the off-axispeak does not impact the cavity before reaching the bank. Also, anyemission anywhere on the sub-pixel, the off-axis emission impacts notmore than once on the cavity.

In various implementations of the present disclosure, the bank andemission size have an optimum size beyond which the efficiency andcollimation significantly reduces, and the colour shift changes. Thus,for a given resolution of the panel, more than one sub-pixel is neededin one independently controllable emission area. Each sub-pixel is notindependently controllable with respect to their emission. In variousimplementations of the present disclosure, preferred shapes forsub-pixels, whereby the efficiency is maximised, colour shift isminimised and the tolerance on pixel size is maximised, are describedand shown.

In various implementations of the present disclosure, emissions may bein all directions (to maximise brightness for a smartphone, forexample), or in only one direction (for example for a TV, where a broademission in only one direction is required).

In the present disclosure, the size of the emissive area may beconfigured such that the number of times that the off-axis emissionreflected within the filler material to be not more than once beforereaching the bank to improve efficiency, peak brightness, colour shiftvalues, and significantly improves tolerance to the pixel size of thevalues above.

In the present disclosure, the size of the emissive area may beconfigured by a minimum sub-pixel emission width of a pixel, which isdetermined by a thickness of the filler material immediately above thesub-pixel stack, and an angle between the on-axis emission and theoff-axis emission. In the present disclosure, the filler material mayhave a thickness from 1.5 μm to 5 μm, and an angle (e.g., depending onrefractive index of the filler material) between 50° and 60°, while thebank may have an angle from the horizontal of around 20-30°. In thepresent disclosure, a preferable minimum sub-pixel emission width may beless than 13.3 μm, which is independent of colour and refractive indexof the filler material, and the thickness may be preferable 2.5 μm andthe angle may preferably be 53°.

With a white RGB pixel where the colour sub pixels have a pitch of 13.3μm in one direction (e.g., x-axis), an example emissive display wouldindicate a resolution more than 1900 colour dots per inch (dpi), takingthe width of a bank between pixels into account, in such direction. Suchan arrangement may have a very high resolution and lower resolutions maybe desirable where cost is important. With a plurality of sub-pixelstacks being controlled by the same control signal to replace a singlewhite pixel in the example emissive display, for example, three sets offour adjacent sub-pixels stacks arranged in an array and controlledunder the same control signal (e.g., FIG. 8A), the example emissivedisplay would give a lower resolution.

According to the present disclosure, on-axis brightness is maximized aswell as the brightness perceived by the user even if total light outputefficiency is not maximized Since light of the on-axis emission isgenerally perceived by a user at a central area of a pixel and light ofthe off-axis emission is generally perceived at edges of a bank, adistribution of light from these different spectral areas may provide amore balanced colour distribution at all angles, thereby minimisingcolour shift at various angles.

FIG. 1A is a schematic cross-sectional view of a portion of an examplelight emitting structure in accordance with an example implementation ofthe present disclosure. In FIG. 1A, an example structure 100 may includea substrate 102, a sub-pixel stack 104, a bank 106, a first fillermaterial 110, a second filler material 112, and a glass cover 122. Inone or more implementations of the present disclosure, the first fillermaterial 110 may be a higher refractive index material, and the secondfiller material 112 may be a lower refractive index material relative tothe first filler material 110. The sub-pixel stack 104 may be disposedon the substrate 102 with the bank 106 surrounding the sub-pixel stack104 to form an interior space 108 above the sub-pixel stack 104. In oneimplementation, the example structure 100 may include a pixel structure.

In the present implementation as shown in FIG. 1A, the first fillermaterial 110 may be disposed in the interior space 108 that is formed bythe bank 106 surrounding the sub-pixel stack 104. The second fillermaterial 112 may be disposed continuously over the first filler material110 and the bank 106.

In another implementation, the second filler material 112 may bepartially disposed on the first filler material 110. In one or moreimplementations, the bank 106 may be greater in thickness than thethickness of the first filler material 110. In one or moreimplementations, the bank 106 is in contact with the substrate 102. In apreferred implementation, the bank 106 may be in contact or almost incontact with the second filler material 112. In one or moreimplementations, the glass cover 122 may be disposed continuously overthe second filler material 112.

In one or more implementations, light is emitted from the sub-pixelstack 104 through the first filler material 110, the second fillermaterial 112, and the glass cover 122. The first filler material 110 mayhave a higher refractive index than air so that the first fillermaterial 110 may extract light from the sub-pixel stack 104 to a greaterextent than air as a filler material. Light trapped in the sub-pixelstack 104 may be quickly absorbed while light trapped in the firstfiller material 110 may propagate to edges of the bank 106 and beextracted by reflection.

In one or more implementations, the first filler material 110 may have ahigher refractive index than those of the sub-pixel stack 104 and thesecond filler material 112. In one implementation, the second fillermaterial 112 (e.g., a lower refractive index layer) may be an air gap.In one or more implementations, the bank 106 may be opaque. A surface ofthe bank 106 facing the first filler materials 110 may be scatteringreflective or specular reflective, and may be at an angle (e.g., sloped)with respect to the plane of the substrate 102 (e.g. a glass substrate).

FIG. 1B is a schematic cross-sectional view of a portion of thesub-pixel stack in the light emitting structure of FIG. 1A in accordancewith an example implementation of the present disclosure. As shown inFIG. 1B, the sub-pixel stack 104 includes a first electrode layer 104 a,an ETL layer 104 b, an emissive layer 104 c, an HTL layer 104 d, and asecond electrode layer 104 e.

In one example implementation, with reference to FIGS. 1A and 1B, thefirst filler material 110 may be disposed on the first electrode layer104 a of the sub-pixel stack 104 and the refractive index of the firstelectrode layer 104 a may be substantially the same as the refractiveindex of the first filler material 110. In the present implementation,the first electrode layer 104 a may be a transparent top electrode andthe second electrode layer 104 e may be a bottom reflective electrode.The first electrode layer 104 a may be a cathode layer that isnon-metallic, substantially transparent, and disposed on the ETL layer104 b. The second electrode layer 104 e may be disposed on the substrate102 and may be an anode layer that is a metallic reflector reflectinglight emitted from the emissive layer 104 c.

However, the arrangement of the first electrode layer 104 a and thesecond electrode layer 104 e is not limited to the examples providedherein and may be reversed. For example, the first electrode layer 104 amay be a bottom anode layer that is a metallic reflector reflectinglight emitted from the emissive layer 104 c and the second electrodelayer 104 e may be a top cathode layer that is non-metallic andsubstantially transparent.

As shown in FIG. 1B, the HTL layer 104 d may include a TFB layer 104 d 1and a PEDOT:PSS layer 104 d 2. In another implementation, the HTL layer104 d may include other layers and is not limited to the example layersprovided herein. For example, a third layer may exist in the HTL layer104 d between the bottom reflector and the PEDOT:PSS layer 104 d 2. Thethird layer may be of Indium Tin Oxide (ITO) or Indium Zinc Oxide (IZO).In another implementation, the previous arrangements of the HTL layer104 d and the ETL layer 104 b may be reversed depending on thearrangements of the first electrode layer 104 a and second electrodelayer 104 e.

In one or more implementations of the present disclosure, with referenceto FIGS. 1A and 1B, at least one single emission peak is produced fromthe sub-pixel stack 104. With reference to FIG. 1A, a main portion 114of the emission peak (hereinafter a first emission peak 114) and otherportions 116 of the emission peak (hereinafter a second emission peak116) may be produced from the sub-pixel stack 104. The first emissionpeak 114 may be an on-axis emission that is emitted from the emissivelayer 104 c, normal to a top surface of the emissive layer 104 c,through the ETL layer 104 b, the first electrode layer 104 a, and thenthrough the first filler material 110, the second filler material 112,and the glass cover 122 substantially without total internal reflection.

In one or more implementations of the present disclosure, the secondemission peak 116 may be an off-axis emission emitted from the emissivelayer 104 c and into the first filler material 110 at an off-angle withrespect to the first emission peak 114. The off-axis second emissionpeak 116 may reflect totally and internally at the interface 120 (e.g.,the top surface of the first filler material 110) at least once as atotal internal reflection (TIR) 118, before reaching a sloped sidewall107 of the bank 106. The off-axis second emission peak 116 undergonetotal internal reflection may reflect off the sloped sidewall 107 alongthe on-axis direction (e.g., at an angle that is normal to the topsurface of the emissive layer 104 c) and through the interface 120substantially without total internal reflection.

In one or more implementations, the first emission peak 114 may beemitted through the interface 120 substantially without total internalreflection. In a preferred implementation, a bank angle θ_(B) of thesloped sidewall 107 is one-half an off-axis second emission peak angleθ_(P) with respect to the on-axis first emission peak 114. With thisarrangement, a high on-axis brightness is achieved.

FIG. 2A illustrates a portion of an example light emitting structure inaccordance with an example implementation of the present disclosure.FIG. 2B illustrates an example emission distribution diagram of thelight emitting structure in FIG. 2A in accordance with an exampleimplementation of the present disclosure.

In FIG. 2A, an example structure 200A may include a sub-pixel stack 204which emits a plurality of light emissions including at least one singlemain emission peak, a first filler material 210, a second fillermaterial 212, an interface 220, and a glass cover 222. In one or moreimplementations, the sub-pixel stack 204, the first filler material 210,the second filler material 212, the interface 220, and the glass cover222 may correspond to the sub-pixel stack 104, the first filler material110, the second filler material 112, the interface 120, and the glasscover 122, respectively, of the example structure 100 in FIG. 1A.

In FIG. 2A, the example structure 200A has a first electrode layer thatmay include a transparent top electrode layer, a second electrode layerthat may be a reflective bottom electrode layer, and the interface 220(e.g., a surface of the first filler material 210). As described above,a single main emission peak is produced by the emissive layer. A mainportion 214 of the main emission peak (e.g., the straight arrow in FIG.2A) passes through the first filler material 210 and second fillermaterial 212 while the other portions of the main emission peak (e.g.,other arrows not labelled in FIG. 2A) spread in various angles whichleads to lower on-axis brightness.

As described above, the main portion 214 of the main emission peak(e.g., the on-axis emission) is emitted through the filler materials210, 212 while the other portions of the emission peak (e.g., theoff-axis emission) are spread in various angles. The on-axis firstemission peak 214 is emitted normal to a top surface of the sub-pixelstack 204 while the off-axis emissions (e.g., other arrows not labelledin FIG. 2A) are emitted into the first filler material 210 at anoff-angle with respect to the on-axis emission. In the presentimplementation, the on-axis emission is a first emission peak 214.

With reference to an example diagram 200B in FIG. 2B, angulardistribution of the main emission peak at one wavelength is measured inthe first filler material 210 of the example structure 200A in FIG. 2A.The on-axis first emission peak 214 and the off-axis emissions of themain emission peak are illustrated in the angular distribution.

FIG. 2C illustrates a portion of another example light emittingstructure in accordance with an example implementation of the presentdisclosure. FIG. 2D illustrates angular distributions of three emissionpeaks measured in the first filler material 210 of the example structure200C in FIG. 2C in accordance with an example implementation of thepresent disclosure.

In FIG. 2C, the example structure 200C may include a similar structureto that of the example structure 200A in FIG. 2A, Therefore, the detailsof the example structure 200C are omitted for brevity.

In contrast to the example structure 200A, the interface 220 (e.g., atop surface of the first filler material 210) in the example structure200C has a higher refractive index. In the example structure 200C, theon-axis first emission peak 214 (e.g., the solid arrow) is emitted fromthe emissive layer of the sub-pixel stack 204 while the off-axisemissions of the main emission peak (hereinafter second emission peak216, e.g., the other solid arrow) is emitted from the sub-pixel stack204 and is totally reflected internally at least once against theinterface 220 via total internal reflection 218 before being reflectedoff a sloped sidewall 207 at an angle that is normal to the top surfaceof the sub-pixel stack 204. In one or more implementations of theinterface 220 (e.g., a surface of the high refractive index first fillermaterial 210), the second emission peaks 216 may be totally reflectedinternally against the interface 220 at least once via total internalreflection 218 before being reflected off the sloped sidewall 207 at thenormal angle.

With such arrangement, higher on-axis brightness is achieved. Incontrast, without the interface 220 (e.g., a surface of the first fillermaterial 210 not having high refractive index), the off-axis emissions(e.g., the dotted line arrow in the example structure 200C) may not betotally reflected internally to the bank but rather may be refracted offthe first filler material 210, the second filler material 212, and theglass cover 222, which may result in a reduced on-axis brightness.

With reference to an example diagram 200D in FIG. 2D, angulardistributions of three emission peaks are measured in the first fillermaterial 210 of the example diagram 200D in FIG. 2D. The example diagram200D illustrates the on-axis first emission peak 214 and the off-axisemissions that underwent TIR thus resulting in being two second emissionpeaks 216 planking the on-axis first emission peak 214.

FIG. 3 illustrates example diagrams 300A, 300B, and 300C of angulardistribution from a light emitting structure in accordance with anexample implementation of the present disclosure. It should be notedthat the example diagrams 300A, 300B, and 300C described in FIG. 3 maysubstantially correspond to the example diagrams 200B and 200D describedin FIG. 2. Therefore, the details of the example diagrams 300A, 300B,and 300C are omitted for brevity.

There are bound to be constructive interferences between the lightemission peaks. These interferences are wavelength dependent andmaterials are generally dispersive in their nature towards thepropagation of light. Light emissions from the emissive layers follow afinite spectra width in a calculation related to maximising efficiencyand on-axis brightness. A high variability of a white point is seen as afunction of polar angle. In one or more implementations of the presentdisclosure, the light emitting structure maximises on-axis brightnessand minimises colour shift.

In FIG. 3, the example diagram 300A illustrates a real emission spectrumtypically having a single central peak (or a primary peak if there are aplurality of peaks). A distance between the emitting layer and thebottom electrode layer is chosen so that the relative intensity of theon-axis and off-axis emissions (e.g., the first emission peak 314 andthe second emission peaks 316 in the diagram 300B or 300C) into a fillermaterial (e.g., the high refractive index first filler material) can becontrolled.

The example diagrams 300B and 300C in FIG. 3 illustrate that lightemitted from a sub-pixel stack has a plurality of wavelengths in whichthere is a central wavelength. In an example implementation, most of thelight emission wavelengths that are emitted by the sub-pixel stack areshorter (e.g., 316 in the example diagram 300B) than the centralwavelength (e.g., 314 in the example diagram 300B) while the centralwavelength (or the on-axis emission) is spectrally more intense than theshorter wavelengths (or the off-axis emission). In another exampleimplementation, most of the light emission wavelengths emitted by thesub-pixel stack are longer (e.g., 316 in the example diagram 300C) thanthe central wavelength (e.g., 314 in the example diagram 300C) and thecentral wavelength (or the on-axis emission) is spectrally less intensethan the shorter wavelengths (or the off-axis emission). Since lightemissions from the on-axis emission come from a bulk area of a pixelwhile light from the off-axis emission appears to come from edges of thepixel, light emission may balance out to achieve a low colour shift atvarious angles although each emission may have different spectra.

FIG. 4A is a schematic cross-sectional view of an example structure 400Aof a light emitting structure in accordance with an exampleimplementation of the present disclosure. The example structure 400A inFIG. 4A includes a glass substrate 402, a sub-pixel stack 404, a bank406, a first filler material 410, a second filler material 412, and aglass cover 422. The example structure 400A may substantially correspondto the example structure 100 described in FIG. 1A. Therefore, thedetails of the example structure 400A are omitted for brevity.

In FIG. 4A, the example structure 400A differs from the examplestructure 100 in FIG. 1A since the example structure 400A includes threelight emitting structures 400B, 400C, and 400D (e.g., three sub-pixelstacks) for three different pixels. In one or more implementations ofthe present disclosure, the example structure 400A may include theexample structure 400B for a blue pixel, the example structure 400C fora green pixel, and the example structure 400D for a red pixel. Inanother implementation, the example structure 400A may include more thanthree example structures for more than three pixels, and is not limitedto the described example.

In one or more implementations, a first emission peak 414 is emitted inthe on-axis direction through both the first filler material 410 and thesecond filler material 412 substantially without total internalreflection 418. A second emission peak 416 is emitted from the sub-pixelstack 404 at an off-axis direction towards an interface 420 (e.g., a topsurface of the first filler material 410) between the first fillermaterial 410 and the second filler material 412 and is totallyinternally reflected (e.g., 418) by the interface 420 at least oncebefore being reflected from a sloped sidewall 407 of the bank 406 alongthe on-axis direction substantially without total internal reflection418.

FIGS. 4B, 4C, and 4D are detailed schematic cross-sectional views ofthree example structures 400B, 400C, and 400D (e.g., three dottedcircles) of three sub-pixel stacks in the light emitting structure ofFIG. 4A in accordance with an example implementation of the presentdisclosure. The example structures 400B-400D are example sub-pixelstacks 404 each including a first electrode layer 404 a, an ETL layer404 b, an emissive layer 404 c, a HTL layer 404 d including a TFB layer404 d 1 and a PEDOT:PSS layer 404 d 2, and a second electrode layer 404e. The example structures 400B-400D may substantially correspond to theexample structure 100 described in FIG. 1B. Therefore, the details ofthe example structures 400B, 400C, and 400D are omitted for brevity.

The three example structures 400B-400D are sub-pixel stacks 404 forthree colour pixels (e.g., blue, green, and red pixels respectively).The distance between an emissive layer and a reflective electrode at thebottom of the emitting structure, or a thickness of the HTL layer, maybe tuned such that the constructive on-axis first emission peaks 414 andthe off-axis second emission peaks 416 are emitted.

In one or more implementations, the TFB layers 404 d 1 of the threeexample sub-pixel stacks 400B-400D have different thicknesses such thattuning the thickness t (e.g., t_(B), t_(G), and t_(R)) of each of theTFB layers 404 d 1 may alter the relative intensities of the firstemission peak 414 and the second emission peak 416 in each of theexample sub-pixel stacks 400B-400D. Therefore, the overall brightness isadjusted, and colour shift is reduced.

In one example implementation, the thickness t_(B) of the TFB layer 104d 1 in the example structure 400B for the blue pixel (emitting a centralwavelength at about 435 nm) is about 75 nm, the thickness t_(G) of theTFB layer 104 d 1 in the example structure 400C for the green pixel(emitting a central wavelength at about 530 nm) is about 115 nm, and thethickness t_(R) of the TFB layer 104 d 1 in the example structure 400Dfor the red pixel (emitting a central wavelength at about 620 nm) isabout 150 nm. In a preferred implementation, the thickness or thedistance between the emissive layer and the reflective electrode is 0.53of a wavelength for each of the blue, green, and red pixels whenrefractive index is considered. The offset between the distances of thepreferred implementation (where distance is 0.53) and an idealimplementation (where distance is 0.78) results from the reflectiveelectrodes used. In the example implementation, the example structures400B, 400C, and 400D respectively shown in FIGS. 4B, 4C, and 4D vary inthickness in only one of the layers (e.g., the TFB layer 404 d 1) of theHTL layer 404 d. However, in one or more implementations of the presentdisclosure, any or all layers of the HTL layer 404 d may vary inthickness such that a total optical thickness is the same as the totaloptical thickness if only one of the HTL layer 404 d changes inthickness.

FIG. 5 is a schematic cross-sectional view of an example structure 500of a light emitting structure in accordance with an exampleimplementation of the present disclosure. The example structure 500includes a glass substrate 502, a sub-pixel stack 504, a bank 506, afirst filler material 510, a second filler material 512, and a glasscover 522. The example structure 500 may substantially correspond to theexample structure 100 described in FIG. 1A. Therefore, the details ofthe example structure 500 are omitted for brevity.

In one or more implementations, the example structure 500 differs fromthe example structure 100 in FIG. 1A in that the example structure 500has a second filler material 512 that partially covers the first fillermaterial 510. In one or more implementations, the second filler material512 (e.g., having lower refractive index) partially covers portions ofthe first filler material 510 (e.g., having higher refractive index) toreduce Fresnel reflection loss. Fresnel loss is a fractional loss wherea fraction of light passing through is instead reflected. The reflectedlight bounces around and does not contribute to the peak brightness,thus, a fractional loss. The amount of reflected light depends on thedifference in reflective indices of the filler materials 510, 512, forexample, a smaller difference in refractive indices may reduce loss.

In the present implementation, the second filler material 512 covers amajority of the surface area (e.g., a plane parallel to the X-Y plane)of the first filler material 510 except for peripheral portions of thefirst filler material 510 immediately proximate the bank 506. Therefore,no second filler material 512 (e.g., a lower refractive index layer) aredisposed immediately over the bank 506 such that Fresnel loss due tolight reflected from the bank 506 may be prevented.

The first emission peak 514 may be emitted through an interface 520along the on-axis direction in a central region of the example structure500. The second emission peak 516 may be emitted at an off-axisdirection and reflected by the interface 520 at least once via totalinternal reflection 518 before reaching a sloped sidewall 507 of thebank 506 and being emitted through the interface 520 along the on-axisdirection at the peripheral portions of first filler material 510immediately proximate to the sloped sidewall 507. This leads to higherefficiency, increase in on-axis brightness, and reduction in off-axiscolour shift at various angles.

In another implementation, the second filler material 512 may only covera surface area substantially over a central portion of the first fillermaterial 510. The physical arrangement(s) of the second filler material512 with respect to the first filler material 510 is not limited to theexample arrangements. The second filler material 512 may partially coverthe first filler material 510 in another manner not described.

FIG. 6 is a schematic cross-sectional view of an example structure 600of a light emitting structure in accordance with an exampleimplementation of the present disclosure. The example structure 600includes a glass substrate 602, a sub-pixel stack 604, a bank 606, afirst filler material 610, a second filler material 612, and a glasscover 622. The example structure 600 may substantially correspond to theexample structure 100 in FIG. 1A. Therefore, the details of the examplestructure 600 are omitted for brevity.

In one or more implementations, the example structure 600 differs fromthe example structure 100 in FIG. 1A since the example structure 600 hasa second filler material 612 that partially covers the first fillermaterial 610, the first filler material 610 and second filler material612 both occupy an interior space 608, and a portion of an interface 620between the first filler material 610 and the second filler material 612may be at an angle, specifically interface angle θ_(I), with referenceto a top surface of the sub-pixel stack 604. A correlation between abank angle θ_(B) of a sloped sidewall 607, the interface angle θ_(I),and an off-axis second emission peak angle θ_(P) with respect to anon-axis first emission peak 614 can be represented by the equation:θ_(B)=θ_(I)+(θ_(P)/2)  Equation (3).

In the example structure 100 in FIG. 1A, the interface angle θ_(I) iszero since the interface 120 between the first filler material 110 andsecond filler material 112 is parallel with respect to the top surfaceof the sub-pixel stack 104. Therefore, the Equation (3) may be reducedto θ_(B)=(θ_(P)/2). In other words, the bank angle θ_(B) in the examplestructure 100 is twice the second emission peak angle θ_(P) in theexample structure 100.

In one or more implementations, a portion of the interface 620 betweenthe first filler material 610 and the second filler material 612immediately proximate the sloped sidewall 607 is angled upwards towardsthe bank 606. In other words, a portion of the interface 620 immediatelyproximate to the sloped sidewall 607 is at an angle, specifically theinterface angle θ_(I), with respect to a top surface of the sub-pixelstack 604 as shown in FIG. 6.

The interface 620 with the interface angle θ_(I) has a sloped surfacearea (e.g., a plane between the Y-Z plane and the X-Y plane). The slopedsurface area of the interface 620 is where the last reflection via totalinternal reflection 618 of second emission peak 616 occurs beforereaching the sloped sidewall 607 of the bank 606. The extent of thesloped surface area of the interface 620 depends on a distance D_(BS)from a top surface of the bank 606 to the onset of the sloped surfacearea of the second filler material 612. In one preferred implementation,with reference to FIG. 6, a distance D_(BS) correlates to a totalthickness T_(AF) and the bank angle θ_(B). The total thickness T_(AF) isa sum of a thickness of the first filler material 610 (e.g., thethinnest part of the first filler material 610) and a thickness T_(2f)of the second filler material 612 near the centre of the first andsecond filler materials 610, 612. Moreover, a distance D_(F) correlatesto the thickness T_(2f) and the interface angle θ_(I) or to the totalthickness T_(AF), the thickness T_(2f) of the second filler material612, the off-axis second emission peak angle θ_(P) with respect to theon-axis first emission peak 614, and the interface angle θ_(I) in thefollowing equations:D _(BS) =T _(AF)/tan(θ_(B))  Equation (4)D _(F) =T _(2f)/tan(θ_(I))=(T _(AF) −T_(2f))*tan(θ_(P)+2θ_(I))  Equation (5).

By adjusting the various parameters above, the preferred bank angleθ_(B) may be obtained.

In one or more implementations, the bank angle θ_(B) may be narrow. Inone preferred implementation, the bank angle θ_(B) is approximately20-40° such that the bank 606 of a pixel may have a larger bank surfacearea (e.g., a plane of the sloped sidewall 607 between the Y-Z plane andthe X-Y plane in FIG. 6) than another bank surface area with a widerbank angle. For emissive displays such as QLEDs, there is a limit to thesurface brightness that can be achieved since higher surface brightnesscan lead to lower product life. Therefore, a narrow bank angle and highbank surface area can reduce the overall brightness while improvingon-axis brightness.

In one or more implementations, after the off-axis second emission peak616 totally and internally reflects (618) at least once against theportion of the interface 620 immediately proximate the sloped sidewall607, the angle of the second emission peak 616 changes on its lasttotally internal reflection 618 resulting in the second emission peak616 being emitted along the on-axis direction. A narrower bank angle andlarger projected bank surface area provide preferred collimatedperformances.

In one or more implementations of the present disclosure, the topemitting structure having an ITO top transparent electrode provides ahigher collimation ratio, e.g., 2.26, compared to the collimation ratioof 1, for a Lambertian source. A standard LCD backlight with brightnessenhancement films has a collimation ratio of about 3 to 3.5, anOLED/QLED with a typical interior space structure (e.g., cavitystructure) and a metal top electrode has a collimation ratio of about 2,and an OLED/QLED with a transparent ITO top electrode (providing bettercolour shift and efficiency than the cavity structure) has a collimationratio of about 1.03.

FIG. 7A is a schematic cross-sectional view of another example lightemitting structure 700A in accordance with an example implementation ofthe present disclosure. The example structure 700A includes a glasssubstrate 702, a sub-pixel stack 704, a bank 706 having a slopedsidewall 707, a cavity 708, a first filler material 710, a second fillermaterial 712, an interface 720 between the first filler material 710 andthe second filler material 712, and a glass cover 722. The examplestructure 700A may substantially correspond to the example structure 100described in FIG. 1A. Therefore, the details of the example structure700A are omitted for brevity.

In one or more implementations, the sub-pixel stack 704 of the examplestructure 700A may include an emissive area 724A (e.g., a top surfacearea of the sub-pixel stack 704 in FIG. 7A) from which on-axis firstemission peaks and off-axis second emission peaks may emit. The size ofan emission area may be configured such that at least one of the secondemission peaks is reflected by an interface not more than once beforereaching a sloped sidewall of a bank. In the example structure 700A, theemission area 724A may emit an on-axis first emission peak 714 a (e.g.,a dotted-line arrow) and an off-axis second emission peak 716 (e.g.,solid arrows 718 a and 716), and the second emission peak 716 may betotally reflected internally not more than once against the interface720 via total internal reflection 718 a before being reflected off thesloped sidewall 707 at an angle that is normal to the top surface of thesub-pixel stack 704. For second emission peaks to reflect not more thanonce against the interface 720, the size of the emission area 724A maybe determined by a minimum sub-pixel emissive width, W, of the emissivearea 724A. The minimum width, W, correlates to a thickness T_(1f) of thefirst filler material 710 and an angle θ_(P) between the on-axisdirection of the first emission peak 714 a and the off-axis direction ofthe second emission peak 716 from the emissive area 724A (e.g.,direction along the arrow indicated by 718 a) in the following equation:W=4*T _(1f)*tan(θ_(P))  Equation (6).

In other implementations, the emission area 724A may emit anotheron-axis first emission peak 714 b and an off-axis second emission peak716 (e.g., propagating along the arrows 718 b, 718 a, and 716). Thesecond emission peak 716 may be totally reflected internally against theinterface 720 via total internal reflection (e.g., 718 b and 718 a)before being reflected off the sloped sidewall 707 at an angle that isnormal to the top surface of the sub-pixel stack 704.

FIG. 7B is a schematic cross-sectional view of another example lightemitting structure in accordance with an example implementation of thepresent disclosure. The example structure 700B may substantiallycorrespond to the example structure 700A described in FIG. 7A.Therefore, the details of the example structure 700A are omitted forbrevity.

In one or more implementations with reference to the example structure700B in FIG. 7B, an emission area 724B of a sub-pixel stack 704 may emitan on-axis first emission peak 714 c (e.g., a solid arrow) and anoff-axis second emission peak 716 c (e.g., solid arrows 718 c and 716c). The second emission peak 716 c may be totally reflected internallynot more than once against the interface 720 via total internalreflection (e.g., solid arrow 718 c) before being reflected off thesloped sidewall 707 at an angle that is normal to the top surface of thesub-pixel stack 704.

In other implementations, the emission area 724B may emit anotheron-axis first emission peak 714 d and an off-axis second emission peak716 d (e.g., dotted line arrows 718 d and 716 d). The second emissionpeak 716 d is also totally reflected internally not more than onceagainst the interface 720 via total internal reflection (e.g., dottedline arrow 718 d) before being reflected off the sloped sidewall 707 atan angle that is normal to the top surface of the sub-pixel stack 704.

As shown in FIG. 7B, not only light emission from the centre of thesub-pixel in at least one direction from the off-axis peak does notimpact the cavity before reaching the bank, but also the off-axisemission impacts not more than once on the cavity for any emissionanywhere on the sub-pixel.

FIG. 8A is a schematic perspective view of an example light emittingstructure 800 in accordance with an example implementation of thepresent disclosure. FIG. 8B is a schematic top view of the lightemitting structure 800 of FIG. 8A.

In one or more implementations of the present application, the lightemitting structure 800 may include a plurality of sub-pixel stacksarranged in a two-dimensional (2-D) array (e.g., a rectangular array).As illustrated in FIGS. 8A and 8B, the light emitting structure 800includes three sets of four adjacently arranged sub-pixel stacks eachset emitting a different colour (e.g., four red sub-pixel stacks on theleft, four green sub-pixel stacks in the middle, and four blue sub-pixelstacks on the right). Each of the three sets of sub-pixel stacksemitting the same colour may constitute one active area, and may becontrolled by the same control signal such that all sub-pixel stacksemitting the same colour function as one pixel with equivalentstructures and uniform emissions.

As shown in FIGS. 8A and 8B, each sub-pixel stack 804 may include anemissive area 824 and a bank 806 surrounding the sub-pixel stack. Eachsub-pixel stack 804 and corresponding bank 806 may also includesubstantially the same components (e.g., glass substrate, first fillermaterial, second filler material, etc., not explicitly shown) as thoseshown and described with reference to the example structure 100 in FIG.1A. Therefore, the details of the light emitting structure 800 areomitted for brevity.

In one or more implementations, two or more sub-pixel stacks emittingthe same colour that are arranged adjacent to one another and arecontrolled by the same control signal such that the two sub-pixel stackstogether act as one colour pixel with equivalent structures and uniformemissions. For example, a sub-pixel stack emitting one colour (e.g., ared sub-pixel stack 804R₁ on the upper left corner in FIG. 8B) may bearranged adjacent to another sub-pixel stack emitting the same colour(e.g., another red sub-pixel stack 804R₂ immediately to the right of thered sub-pixel stack 804R₁ in FIG. 8B) and the two sub-pixel stacks arecontrolled by the same control signal. In another implementation, thelight emitting structure 800 may include at least four sub-pixel stacksemitting the same colour that are arranged adjacent to one another in arectangular array (e.g., red sub-pixel stacks 804R₁, 804R₂, 804R₃, and804R₄ in FIG. 8B) and are controlled by the same control signal.

In the present implementation, the light emitting structure 800 mayinclude three sets of four adjacently arranged sub-pixel stacks emittingthree different colours (e.g., four sub-pixel stacks R′ including fourred emissive areas 824 on the left, four sub-pixel stacks G′ includingfour green emissive areas 824 in the middle, and four sub-pixel stacksB′ including four blue emissive areas 824 on the right in FIG. 8B). Inthe present implementation, each of the three sets of four adjacentlyarranged sub-pixel stacks has a rectangular array. However, the shape ofthe array is not limited to the example provided herein. For example,each set of four adjacently arranged sub-pixel stacks in the lightemitting structure 800 may have a square, triangular, or hexagonalarray. In the present implementation, each emissive area 824 may have arectangular shape in FIG. 8B. However, the shape of each emissive area824 is not limited to the example provided herein. In the presentimplementation, the minimum pixel emissive width W of each rectangularemissive area 824 is a distance in the x-direction.

FIG. 9A is a schematic top view of an example light emitting structure900A in accordance with an example implementation of the presentdisclosure. As shown in FIG. 9A, the light emitting structure 900A mayinclude a plurality of sub-pixel stacks each having an emissive area 924and a bank 906. The light emitting structure 900A may includesubstantially the same components (e.g., glass substrate, first fillermaterial, second filler material, etc., not shown) as the light emittingstructure 800 described in FIGS. 8A and 8B. Therefore, the details ofthe light emitting structure 900A are omitted for brevity. The lightemitting structure 900A differs from the light emitting structure 800 inthat each sub-pixel stack and the corresponding emissive area 924 in thelight emitting structure 900A may have an elongated rectangular shape.It should be noted that the shape of each emissive area 924 is notlimited to the example provided herein. In the present implementation,the minimum pixel emissive width, W, of each elongated rectangularemissive area 924 is a distance in the x-direction.

In some implementations (e.g., in FIGS. 8A, 8B, and 9A), the banks arein contact with one another at the top edge. In some implementations,each two adjacent banks may be separated by a gap.

FIG. 9B is a schematic cross-sectional view of the example lightemitting structure 900A of FIG. 9A along line A-A′ in accordance with anexample implementation of the present disclosure. As shown in FIG. 9B,the light emitting structure 900B may include a glass substrate 902, twosub-pixel stacks 904R, banks 906, a first filler material 910, a secondfiller material 912, an interface 920 between the first filler material910 and the second filler material 912, and a glass cover 922. Each ofthe two sub-pixel structures in the light emitting structure 900B maysubstantially correspond to the sub-pixel structure shown in the lightemitting structure 100 in FIG. 1A. Thus, the details of the sub-pixelstructure are omitted for brevity.

In one or more implementations, each sub-pixel stack 904R of the examplestructure 900B may include an emissive area 924 (e.g., a top surfacearea of the sub-pixel stack 904R in FIG. 9B) from which on-axis firstemission peaks and off-axis second emission peaks may emit. The size ofthe emission area 924 may be configured such that at least one of thesecond emission peaks is reflected by an interface not more than oncebefore reaching a sloped sidewall of a bank. In the example structure900B, the emission area 924 may emit an on-axis first emission peak 914and an off-axis second emission peak 916, where the second emission peak916 may be totally reflected internally not more than once against theinterface 920 via total internal reflection 918 before being reflectedoff the sloped sidewall 907 at an angle that is normal to the topsurface of the sub-pixel stack 904. For the second emission peaks toreflect not more than once against the interface 920, the size of theemission area 924 may be determined by a minimum sub-pixel emissivewidth, W, of the emissive area 924, where W is determined based onEquation (6) above.

In the present implementation, the angular distribution and colour shiftin the x-direction may be more important than the y-direction. Thus, thesecond emission peaks are reflected not more than once against theinterface 920 in the x-direction, which is achieved by configuring theminimum sub-pixel emissive width, W, in the x-direction. In the presentimplementation, the two sub-pixel structures in the light emittingstructure 900B are controlled by the same control signal 940 to emit thesame colour. In the present implementation, the resolution in thex-direction (for three colours, having two sub-pixels per colour) mayreduce the resolution (white pixels) to a level that is more achievable.

It should be noted that the banks in FIG. 9A are shown to be touchingeach other at the top edge. In some implementations, there may be a gapbetween the tops of banks, and the active area and bank height may besmaller than shown here. The overall patterns and shapes should be thesame and is assumed for all shapes and patterns described in the presentdisclosure. It is also possible that all the layers from the cavity arecontinuous over the bank separating two non-independent sub-pixels.

FIG. 10 is a schematic top view of an example light emitting structure1000 in accordance with an example implementation of the presentdisclosure. In the present implementation, the light emitting structure1000 may include three sets of four adjacently arranged sub-pixel stackseach set emitting a different colour (e.g., four red sub-pixel stacks R′on the left, four green sub-pixel stacks G′ in the middle, and four bluesub-pixel stacks B′ on the right). In the present implementation, eachof the three sets of four adjacently arranged sub-pixel stacks has acircular shape, and is arranged in a closely-packed 2-D array. Each setof the four adjacently arranged sub-pixel stacks may be controlled bythe same control signal such that the four sub-pixel stacks together actas one pixel with equivalent structures and uniform emissions. It shouldbe noted that the shape of the array is not limited to the examplesprovided herein. For example, each of the sub-pixel stacks in theexample structure 1000 may have a square, triangular, or hexagonalshape. In the present implementation, each sub-pixel stack, eachcorresponding emissive area 1024, and each corresponding bank 1006 mayhave a circular shape. However, the shape is not limited to the examplesprovided herein. In the present disclosure, the closely-packed-circulararray with the circular sub-pixel stacks, emissive areas, and banks maybe a preferred arrangement to further reduce visibility of the pixelarray for smartphone and VR applications. In the present implementation,the minimum pixel emissive width W of each emissive area 1024 is adiameter of the circular emissive area.

FIG. 11 is a schematic top view of an example light emitting structure1100 in accordance with an example implementation of the presentdisclosure. In the present implementation, the light emitting structure1100 may include three sets of two adjacently arranged sub-pixel stackseach set emitting a different colour (e.g., two red sub-pixel stacks R′on the left, two green sub-pixel stacks G′ in the middle, and two bluesub-pixel stacks B′ on the right). In the present implementation, eachof the three sets of two adjacently arranged sub-pixel stacks has anelliptical shape and is arranged in a 2-D array. Each set of the twoadjacently arranged sub-pixel stacks may be controlled by the samecontrol signal such that the two sub-pixel stacks together act as onepixel with equivalent structures and uniform emissions. It should benoted that the shape of the array is not limited to the example providedherein. For example, each of the sub-pixel stacks in the examplestructure 1100 may have a square, triangular, or hexagonal shape. In thepresent implementation, each sub-pixel stack, each correspondingemissive area 1124, and each corresponding bank 1106 may have anelliptical shape. However, the shape is not limited to the examplesprovided herein.

With reference to FIG. 9A, a rectangular sub-pixel of the light emittingstructure 900A is an elongated version of a rectangular pixel of lightemitting structure 800B in FIG. 8B. Similarly, an elliptical sub-pixelin FIG. 11 is an elongated version of a circular sub-pixel in FIG. 10.With the elliptical sub-pixels, collimation is possible in one directionwhile being broad in the another direction, which could be applicable intelevision display viewing where angular breadth in one axis (e.g.,x-axis) is required, but not in the other direction (e.g., y-axis). Thelight in the other direction can be collimated to a greater extent toincrease the brightness of the television display. The horizontal axisof the display (e.g., broad) would then be parallel to the long axis(e.g., x-axis) of the elliptical sub-pixels as shown in FIG. 11. In FIG.11, colour stripes are vertical, aligned along the short axis of theelliptical sub-pixels. In contrast, it may be possible to have thecolour stripes aligned along the long axes of the elliptical sub-pixels,which may improve the overall resolution for a red, green, and blue(RGB) display. In the present implementation, the minimum pixel emissivewidth, W, of each elliptical emissive area 1124 is the major axis of theelliptical emissive area 1124 in the x-direction.

FIG. 12 is a schematic top view of an example light emitting structure1200 in accordance with an example implementation of the presentdisclosure. In the present implementation, the light emitting structure1200 may include three sets of sub-pixel stacks each set emitting adifferent colour. In the present implementation, the three sets ofsub-pixel stacks may include sub-pixel stacks of different quantity andsizes. For example, as shown in the example structure 1200, a firstarray 1250R may include six red sub-pixel stacks R′ having small-sizecircular emissive areas 1224R having a minimum width (W_(R)) and banks1206R. The light emitting structure 1200 may include a second array1250G having four green sub-pixel stacks G′ with medium-size circularemissive areas 1224G having a minimum width (W_(G)) and banks 1206G. Thelight emitting structure 1200 may include a third array 1250B havingthree blue sub-pixel stacks B′ with large-size circular emissive areas1224B having a minimum width (W_(B)) and banks 1206B.

In the present implementation, the circular emissive areas 1224R, 1224G,and 1224B have different diameters. In one implementation, it is alsopossible for only one set of sub-pixels to meet the size requirements toensure that the off-axis emissions from the emissive area are reflectedupon the interface not more than once before reaching the slopedsidewall of the bank. According to implementations of the presentdisclosure, absorption in emission cavities may be significantly greaterfor blue colour emissions than for green or red colour emissions. Hence,it is possible for the blue sub-pixels to meet the size requirements ina display and the green and red not to. In some implementations of thepresent disclosure, the size of the emissive area can be smaller as thecavity absorption increases and the number of sub-pixels can be unevenamong different pixel colours. Also, it should be noted that the shapesand sizes of the sub-pixel stacks are not limited to the examplesprovided herein.

FIG. 13 is a schematic top view of an example light emitting structure1300 in accordance with an example implementation of the presentdisclosure. In the present implementation, the example structure 1300may include at least four sets of two adjacently arranged sub-pixelstacks, three of the four sets of two adjacently arranged sub-pixelstacks each emitting a different colour. In the present implementation,the four sets of two adjacently arranged sub-pixel stacks may togetherbe arranged in a diamond interlaced array. For example, two redsub-pixel stacks R (each having an emissive area 1324R and a bank1306R), two green triangular sub-pixel stacks G (each having an emissivearea 1324G and a bank 1306G), two blue triangular sub-pixel stacks B′(each having an emissive area 1324B′ and a bank 1306B′), and another twoblue triangular sub-pixel stacks B″ (each having an emissive area 1324B″and a bank 1306B″), where the four sets of two adjacently arrangedsub-pixel stacks are be arranged together in a diamond interlaced array.However, it should be noted that the shapes and sizes of the sub-pixelstacks are not limited to the examples provided herein. In one or moreimplementations, each set of the two adjacently arranged sub-pixelstacks is controlled by the same control signal. In the presentimplementation, the minimum pixel emissive width, W, of each of thetriangular emissive area 1324R, 1324B′, 1324B″, and 1324G are the same.

Regarding FIGS. 8A, 8B, 9A, 9B, 10, 11, 12, and 13, it should be notedthat the emissive areas and bank heights may be smaller than illustratedin the drawings. The overall patterns (e.g., array) and shapes of theemissive areas and banks should be substantially the same. Moreover, inone or more implementations, all layers above the sub-pixel stack arecontinuously arranged over the bank(s) and separating two sub-pixelsunder the same control signal. In some implementations, it may bepossible for only one set of sub-pixel stacks to meet the size (e.g.,minimum pixel emissive width) requirements above. According toimplementations of the present disclosure, absorption in the cavitystructure (e.g., first filler material) may be significantly greater forblue colour emitting sub-pixel stacks than for the green or red colouremitting sub-pixel stacks. Hence, it is possible for the blue sub-pixelstacks to meet the size requirements in a display while the green andred sub-pixel stacks may not. In some implementations of the presentdisclosure, the size of the sub-pixel stacks may be smaller as thecavity absorption increases. In some other implementations, the numberof sub-pixel stacks may be uneven between sub-pixel stacks of differentcolours. In one or more implementations as shown in FIGS. 8A, 8B, 9A,9B, 10, 11, 12, and 13, it should be noted that the minimum pixelemissive width is configured such that the off-axis emissions from theemissive area are reflected upon the interface not more than once beforereaching the sloped sidewall of the bank.

From the present disclosure, it can be seen that various techniques maybe used for implementing the concepts described in the presentdisclosure without departing from the scope of those concepts. While theconcepts have been described with specific reference to certainimplementations, a person of ordinary skill in the art may recognizethat changes may be made in form and detail without departing from thescope of those concepts.

As such, the described implementations are to be considered in allrespects as illustrative and not restrictive. It should also beunderstood that the present disclosure is not limited to the particularimplementations described but rather many rearrangements, modifications,and substitutions are possible without departing from the scope of thepresent disclosure.

What is claimed is:
 1. A light emitting structure comprising: asubstrate; a sub-pixel stack over the substrate; a bank surrounding thesub-pixel stack on the substrate and forming a cavity above thesub-pixel stack; a first filler material in the cavity; and a secondfiller material over the first filler material; wherein the sub-pixelstack emits a first emission peak along an on-axis directionsubstantially normal to a top surface of the sub-pixel stack, and asecond emission peak along an off-axis direction at an angle to theon-axis direction; wherein the first emission peak emits through aninterface between the first filler material and the second fillermaterial substantially without reflection; wherein the second emissionpeak from the sub-pixel stack is totally reflected by the interface ontoa sloped sidewall of the bank, and the second emission peak reflectedfrom the sloped sidewall of the bank emits along the on-axis directionthrough the interface substantially without reflection; and wherein anemissive area of the sub-pixel stack is configured such that the secondemission peak is reflected by the interface not more than once beforereaching the sloped sidewall of the bank.
 2. The light emittingstructure of claim 1, wherein a minimum width of the emissive area ofthe sub-pixel stack is configured based on a thickness of the firstfiller material, and the angle between the on-axis direction of thefirst emission peak and the off-axis direction of the second emissionpeak.
 3. The light emitting structure of claim 1, wherein: the firstemission peak is emitted through the interface along the on-axisdirection in a central region of the light emitting structure; thesecond emission peak reflected by the sloped sidewall of the bank isemitted through the interface along the on-axis direction in aperipheral region of the light emitting structure; and on-axisbrightness is increased and off-axis colour shift having an angle isreduced.
 4. The light emitting structure of claim 1, wherein: the firstemission peak is emitted through the interface along the on-axisdirection in a peripheral region of the light emitting structureadjacent to a bottom edge of the bank; the second emission peakreflected by the sloped sidewall of the bank is emitted through theinterface along the on-axis direction in another peripheral region ofthe light emitting structure opposite of the peripheral region; andon-axis brightness is increased and off-axis colour shift having anangle is reduced.
 5. The light emitting structure of claim 1, furthercomprising: another sub-pixel stack arranged immediately adjacent to thesub-pixel stack; wherein the another sub-pixel stack emits the firstemission peak and the second emission peak, and has an emissive areasubstantially equal to the emission area of the sub-pixel stack.
 6. Thelight emitting structure of claim 5, wherein the sub-pixel stack and theanother sub-pixel stack are controlled to a same control signal.
 7. Thelight emitting structure of claim 1, wherein the second filler materialhas a second refractive index substantially equal to or lower than afirst refractive index of the first filler material.
 8. The lightemitting structure of claim 1, wherein the emissive area has one of thefollowing shapes: a rectangular shape; a square shape an ellipticalshape; a circular shape; and a triangular shape.
 9. The light emittingstructure of claim 1, wherein an angle between the sloped sidewall ofthe bank and the top surface of the sub-pixel stack is one-half theangle between the on-axis direction of the first emission peak and theoff-axis direction of the second emission peak.
 10. The light emittingstructure of claim 1, wherein the sub-pixel stack comprises: an emissivelayer between a first transport layer and a second transport layer; afirst electrode layer coupled to the first transport layer; and a secondelectrode layer coupled to the second transport layer.
 11. The lightemitting structure of claim 10, wherein: the emissive layer includes aquantum dot emission material; the first transport layer includes a holetransport layer; the second transport layer includes an electrontransport layer; the first electrode layer is an anode layer including ametallic reflector for reflecting the light emitted from the emissivelayer; and the second electrode layer is a cathode layer including anon-metallic and substantially transparent material.
 12. The lightemitting structure of claim 10, wherein: the emissive layer includesquantum dot emission material; the first transport layer includes anelectron transport layer; the second transport layer includes a holetransport layer; the first electrode layer is a cathode layer having ametallic reflector for reflecting the light emitted from the emissivelayer; and the second electrode layer is an anode layer having anon-metallic and substantially transparent material.
 13. A displaydevice comprising the light emitting structure of claim
 1. 14. A lightemitting structure comprising: a substrate; a plurality of sub-pixelstructures over the substrate, each of the plurality of sub-pixelstructures having a same emissive area; wherein at least one of theplurality of sub-pixel structures includes: a sub-pixel stack over thesubstrate; a bank surrounding the sub-pixel stack on the substrate andforming a cavity above the sub-pixel stack; a first filler material inthe cavity; and a second filler material over the first filler material,the second filler material having a second refractive indexsubstantially equal to or lower than a first refractive index of thefirst filler material; wherein the sub-pixel stack emits a firstemission peak along an on-axis direction substantially normal to a topsurface of the sub-pixel stack, and a second emission peak along anoff-axis direction at an angle to the on-axis direction; wherein thefirst emission peak emits through an interface between the first fillermaterial and the second filler material substantially withoutreflection; wherein the second emission peak from the sub-pixel stack istotally reflected by the interface onto a sloped sidewall of the bank,and the second emission peak reflected from the sloped sidewall of thebank emits along the on-axis direction through the interfacesubstantially without reflection; and wherein the second emission peakis reflected by the interface not more than once before reaching thesloped sidewall of the bank.
 15. The light emitting structure of claim14, wherein a minimum width of the emissive area is configured based ona thickness of the first filler material, and the angle between theon-axis direction of the first emission peak and the off-axis directionof the second emission peak.
 16. The light emitting structure of claim14, wherein an angle between the sloped sidewall of the bank and the topsurface of the sub-pixel stack is one-half the angle between the on-axisdirection of the first emission peak and the off-axis direction of thesecond emission peak.
 17. The light emitting structure of claim 14,wherein the emissive areas of the plurality of sub-pixel structures aresubstantially the same, and have one of the following shapes: arectangular shape; a square shape an elliptical shape; a circular shape;and a triangular shape.
 18. The light emitting structure of claim 14,wherein the sub-pixel stack comprises: an emissive layer between a firsttransport layer and a second transport layer; a first electrode layercoupled to the first transport layer; and a second electrode layercoupled to the second transport layer.
 19. The light emitting structureof claim 18, wherein: the emissive layer includes quantum dot emissionmaterial; the first transport layer includes a hole transport layer; thesecond transport layer includes an electron transport layer; the firstelectrode layer is an anode layer including a metallic reflector forreflecting the light emitted from the emissive layer; and the secondelectrode layer is a cathode layer including a non-metallic andsubstantially transparent material.
 20. The light emitting structure ofclaim 18, wherein: the emissive layer includes quantum dot emissionmaterial; the first transport layer includes an electron transportlayer; the second transport layer includes a hole transport layer; thefirst electrode layer is a cathode layer having a metallic reflector forreflecting the light emitted from the emissive layer; and the secondelectrode layer is an anode layer having a non-metallic andsubstantially transparent material.